Three-year evaluation of different adhesion strategies in non-carious cervical lesion restorations: a randomized clinical trial

Abstract: Objective: To evaluate non-carious cervical lesions (NCCLs) restored with different adhesion strategies. Methodology: This is a prospective, randomized, double-blind, split-mouth study. An adhesive restorative system (Single Bond Universal/Filtek Z350XT – SBU) was evaluated both without and with selective enamel conditioning (E-SBU), resin-modified glass-ionomer cements (Vitremer; RMGIC), and ethylenediaminetetraacetic acid pretreatment (EDTA; E-RMGIC). In total, 200 restorations, placed in 50 patients, were evaluated at baseline and at a 3-year follow-up using the modified United States Public Health Service (USPHS) criteria. Data were analyzed using the two-proportion equality test, multinomial logistic regression, Wilcoxon test, and Kaplan-Meier survival curves. Results: In total, 42 (84%) patients returned for the 3-year follow-up. SBU showed restoration losses statistically different from RMGIC. Retention was also statistically different in SBU between baseline and the 3-year follow-up. Marginal defects and surface texture were statistically significant for all groups in the period studied, except for the surface texture of SBU and the marginal integrity in E-RMGIC. We observed no statistically significant difference in wear, secondary caries, anatomical form, surface staining, and color over time. Recession degree was the only factor to influence retention rates. Cumulative survival (%) was 89, 98, 98, and 95.3, for SBU, SE-SBU, RMGIC, and E-RMGIC, respectively, without significant differences among them. There was a statistically significant difference between survival curves; however, multiple comparison procedures found no statistical differences. Conclusion: Selective enamel etching affected the retention of non-carious cervical restorations. Adhesion using EDTA and resin-modified glass-ionomer cements delayed marginal defects over time. The degree of gingival recession influenced retention rates. Resin composite restorations showed initial marginal defects, and ionomer restorations, reduced surface luster. EDTA pre-treatment followed by resin-modified glass-ionomer cements may be a promising adhesion strategy for NCCL restorations.


Introduction
Non-carious cervical lesions (NCCL) are defined as the loss of tooth structure at the cemento-enamel junction area unrelated to dental caries, and their etiology has been described as multifactorial. 1 Resin composites and glass-ionomer cements are currently the material of choice for NCCL restorations. [2][3][4][5][6][7][8][9][10][11] Resin composites have some advantages, such as rapid polymerization, easy handling and reparability, and good mechanical and aesthetic properties; 12 however, they also entail biological effects due to monomers release. 13 This material peculiar features also pose challenges for its adhesion to the dentin substrate in NCCL. 14  Resin-modified glass-ionomer cements (RMGIC) can chemically bond to dental substrates. Since they can mechanically interlock with dentin, they are a good option for restoring NCCLs due to their excellent retention rates: between five and ten years. 16,17 Given the excellent clinical retention of RMGIC -if applied under the manufacturers' instructions, other pretreatment procedures may also be evaluated. The use of ethylenediaminetetraacetic acid (EDTA) before cement application is relevant, given that an in vitro study showed increased bond strength. 18 Moreover, EDTA may be considered a metalloproteinases inhibitor (MMP). 19 Though some clinical trials in the literature evaluate universal adhesives and RMGIC in NCCL restorations separetely, 2,3 studies investigating these adhesion strategies in a same clinical trial after 3 years are scarce. Thus, our research aims to compare these adhesive treatments over time, and the influence of initial characteristics on NCCL restoration retention.
The null hypotheses tested were: (1) the four adhesive strategies would present no statistically significant differences after 3 years, for each clinical criterion and survival analysis; (2) the same adhesive strategy would show no statistically significant difference between baseline and the 3-year follow-up; and (3) the initial characteristics of NCCLs would not influence restoration retention rates after 3 years. degree of sclerosis, 3 as follows: 1 -no evident sclerosis, dentin is opaque, with yellow or whitish discoloration; 2-more than one but less than 50% sclerosis between categories 1 and 4; 3-less than 4, but more than 50% between categories 1 and 4; and 4-significant sclerosis present, dentin has a vitreous, dark yellow or even discolored (brown) appearance, with significant translucency or transparency.
Internal cavity angulation was measured and classified into 45-90°, 90-120°, or >120°. A millimeter probe measured the height, width, and depth of cavities in millimeters. Procedure details can be found in our previous paper. 3

Randomization and restorative procedures
Prophylaxis with a pumice stone and water was performed before the restorative procedures. After color selection, initial photographs were taken; and anesthesia was applied locally when necessary.
Relative isolation was performed using cotton rolls and suction; non-carious cervical lesions underwent no cavity preparation.
Two graduate students identified in the procedure sheet conducted the restorative procedures. One person unrelated to this study prepared opaque sealed envelopes identifying each group by their initials (employed to conceal the randomization sequence).
Treatment was allocated to the groups, a tooth was raffled for one treatment, while the remaining were assigned other treatments, following the split-mouth design. It is important to emphasize that each operator performed the same number of restorative treatments, both for control and test groups.
For the SBU group, the adhesive system (Universal Single Bond -USB, 3M ESPE, St. Paul, USA) was applied to the NCCL under agitation for 20 s on a slightly dry surface followed by a 5-second light air jet. Then, the adhesive system was photocured for 10 s (Radii-cal, 1200 mW/cm 2 , SDI, Victoria, Australia).
For the E-SBU group, the enamel margin was conditioned with 37% phosphoric acid (Total Etch -Ivoclar Vivadent, Liechtenstein) for 15 s, washed with a water jet for 20 s, and slight dried. Then, the USB adhesive system was applied as described above. For the E-RMGIC group, 0.1 M EDTA was applied onto the NCCL surface for 60 s with a brush. Then, the surface was washed with water for 30 s, dried, and restored with RMGIC. In this group, the primer was not applied on the lesion surface to allow the RMGIC to chemically bond to the dentin. The RMGIC were manipulated and inserted as described for Group III.

Clinical evaluation
Restorations were evaluated by visual-tactile inspection using a flat mouth mirror, a periodontal probe, and a dental reflector; and classified according to the modified USPHS criteria. Restorations scored as Alpha or Bravo were considered clinically successful, those scored as Charlie, a failure. Two calibrated evaluators, blind to group assignment, examined and scored the restorations. In eventual disagreements, the evaluators reached a common agreement.
Restorations were evaluated at baseline, and after 1, 2, and 3 years after the procedures.

Statistical analysis
The two-proportions equality test was used to

Results
In total, 50 patients (34 male and 16 female) with a mean age of 61 years (ranging 38-92 years) participated in the study. We performed 200 restorations in total, homogenously distributed patients' initial characteristics within four groups. 3 Three years after the procedures, 42 (84%) patients returned for follow-up. Figure 1 shows restoration and patients' justified absence at each follow-up. We performed no intention-to-treat analysis. Table 1 shows clinical data. SBU contained five lost  Figure 2 shows the statistically significant difference between survival curves (p=0.045); however, multiple comparisons found no statistical differences (p≥0.05). The degree of gingival recession was the only initial characteristic to influence restoration retention (Table 2).

Discussion
Several clinical studies in the literature address non-carious cervical lesions (NCCLs). In restoring these lesions, the chemical interaction with the dental structure is important for the quality and durability of adhesion. 24 Adhesion efficacy improved after the introduction of multi-mode adhesives containing Distinct uppercase letters compare groups by the same evaluation; distinct lowercase letters compare the same group over time.  Retention is one of the most important evaluating criteria for restorative material performance, often used to assess its longevity. The American Dental Association (ADA) guidelines on adhesive materials requires the cumulative 18-month retention rate to be at least 90% for procedures in dentin and enamel to be fully acceptable. 27 However, the guidelines have no requirements for the long-term durability of adhesive systems. In our study, SBU lost approximately 11.9% retention three years after the procedure -the highest value recorded, -thus rejecting the first null hypothesis. Meta-analysis showed universal adhesives to have better adhesion after enamel etching. 28 In that sense, universal adhesives applied through etchand-rinse and selective-etch modes tend to achieve better clinical outcomes. 2,5,6,8 In our study, the group without selective enamel conditioning presented high initial debonding rates, and SBU, the   17 (1) 20 (1) 13 (1) 22 (1) (3) 35 (1) 36 (1) 38 (1)   Approximately 70% of NCCLs restored with RMGIC obtained Alpha scores for marginal discoloration, corroborating the literature results, which verified an Alpha score for this criterion ranging from 42.9% to 84.6% after 5 years of the procedure. 29,33 Studies found restorations that were minimum 2-3 years old in vivo to present an enamel-like layer adjacent to the ionomer due to a calcium and phosphorus increase in this surface layer.
This suggests an additional "mineralization" of the restorative material, 34,35 possibly contributing to its best performance as to its marginal defects. The